                       s)))]
        (step pred coll))))
 
-;; TODO: implement.
+;; TODO: IndexedSeq, cf. #73
 (defn seq
   "Returns a seq on the collection. If the collection is
   empty, returns nil.  (seq nil) returns nil. seq also works on

  ;; TODO: IKVReduce, etc.

  IFn
  ;; TODO: multiple arity protocols
  (-invoke [coll k]
    (-nth coll k))


    (PersistentArrayMap. (hamt/remove k h)))

  IFn
  (-invoke [coll k]
    (-lookup coll k))

